Abstract
In this paper we study some van den Bergh open clusters combining photometry and astrometry. A model which analyses the proper motion distribution and the stellar density is applied to find the kinematic parameters and stellar membership in the region of the open clusters vdB92, vdB146 (NGC 7129) and vdB150. The astrometric data are obtained from UCAC4 catalogue. The centre coordinates, the components of mean proper motion, the angular diameter and the astrometric members are reported, taking the following values: for vdB92: α=105.97281°±0.13113°, δ=−11.57814°±0.10575°, μαcosδ=−3.46±0.19mas/yr,μδ=1.27±0.19mas/yr, 34', 60 members; for vdB146: α=325.78423°±0.15297°, δ=66.13575°±0.02907°, μαcosδ=−2.71±0.25mas/yr, μδ=−3.32±0.25mas/yr, 9', 5 members; and for vdB150: α=332.22519°±0.06074°, δ=73.40232°±0.0.07789°, μαcosδ=3.07±0.90mas/yr, μδ=4.65±0.90mas/yr, 15', 7 members. The incidence of the proper motion errors in the determination of the cluster parameters and of the stellar membership is analysed and it is found that they do not significantly change. We finally compare the astrometric members with the photometric ones given in the literature.
Highlights
The proper motion data are analysed in an elliptical subregion of the Vector Point Diagram (VPD) containing 523 stars
Taking profit that open cluster members share similar photometric and kinematic properties, astrometric and photometric results are combined in this work to reduce the uncertainty introduced by each technique individually
We report that vdB92 has μα cosδc = −3.46 ± 0.19 mas yr, μ=δc 1.27 ± 0.19 mas yr, = σ c 1.44 ± 0.13 mas yr, 60 astrometric members, = αc 105.97281 ± 0.13113, δc = −11.57814 ± 0.10575 and a value of 34' for the diameter
Summary
The analysis of the complex gravitational interactions of their individual members contributes to the study of stellar dynamics. Several of these clusters have been investigated using only photometric techniques to determine the members. As open cluster members share similar photometric and kinematic properties, it is useful to complete the study of the stars of the cluster region by employing astrometric methods. Corti and Orellana [1] and Orellana et al [2] combine astrometric and photometric membership results in order to reduce the uncertainty introduced by each technique individually
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